Sensitive detection of PrPCWD in rectoanal mucosa-associated lymphoid tissue from preclinical white-tailed deer

Authors: Schneider, David; O'Rourke, Katherine; BALACHANDRAN, ARU - Canadian Food Inspection Agency; KEANE, DELWYN - University Of Wisconsin

Submitted to: United States Animal Health Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/11/2009
Publication Date: 10/11/2009
Citation: Schneider, D.A., Orourke, K.I., Balachandran, A., Keane, D. 2009. Sensitive Detection of PrPCWD in Rectoanal Mucosa-Associated Lymphoid Tissue from Preclinical White-Tailed Deer. United States Animal Health Association Proceedings. pg.224-225.

Interpretive Summary: Diagnosis of prion disease [for example, scrapie in sheep and chronic wasting disease (CWD) in elk and deer] relies upon sensitive detection of disease-associated prion protein in the brain or tissues containing lymph follicles. Live animal testing for scrapie disease in sheep has included evaluation of biopsy samples of the tonsil, third eyelid and rectal mucosa. Similarly, diagnosis of CWD in live elk has been recently accomplished through biopsy of the rectal mucosa. This report summarizes the diagnostic performance (test sensitivity) of various tissue sampling sites that were collected after death. The report summarizes the findings from four different populations of white-tailed deer. Two of these populations were from Wisconsin and two from Saskatchewan, Canada; three were captive herds and one consisted of a sample of free-ranging deer. The diagnostic performance of the rectal mucosa samples were similar but lower than that achieved in two other lymphoid tissues, but greater than that achieved in the brain. While these studies were conducted on tissues collected after death, the findings demonstrate the comparative potential for biopsy of the rectal mucosa in live deer not yet showing signs of disease. While many factors may influence test performance in other deer populations, these studies showed that false-negative diagnosis occurred most often in deer presumed to be in an early stage of disease and carrying a mutation in the prion protein gene (codon 96).

Technical Abstract: This report summarizes the comparative diagnostic performance of postmortem rectoanal mucosa-associated lymphoid tissue (RAMALT) sampling in four white-tailed deer test populations: from Wisconsin, a sample of free-ranging deer and a captive herd; and from Saskatchewan, Canada, two captive herds. The apparent prevalence of disease in these test populations ranged from 6-79%. None of these deer were demonstrating signs consistent with CWD. The overall tissue-specific test sensitivities were ranked: RPLN>tonsil>RAMALT>obex. Test sensitivities in captive herd deer having at least one PRNP G96S allele were generally lower but similarly ranked. False negative RAMALT results were associated with early disease progression, as assessed by PrPCWD accumulation scores in RPLN or obex, and/or the PRNP G96S allele. As determined in two of the captive herds, the proportion of CWD-positive RAMALT follicles were generally lowest in deer early in disease progression and/or heterozygous at PRNP codon 96. And, as expected, variation in the proportion CWD-positive RAMALT follicles was inversely related to the total number of observable follicles per sample. These comparisons made on samples collected postmortem suggest general diagnostic evaluation of RAMALT samples in white-tailed deer would have intermediate test sensitivity as compared to evaluation of RPLN and obex. While many factors may influence actual test performance, early stage of disease progression and the PRNP G96S allele are two that were associated with lower test sensitivities.